mating vs sexual activity

mating and sexual activity both are nouns.

Word	Noun	Adjective	Verb	Adverb
mating	Yes	No	No	No
sexual activity	Yes	No	No	No

As nouns, sexual activity is a hypernym of mating; that is, sexual activity is a word with a broader meaning than mating:

Other hypernyms of mating include sex, sex activity, sexual practice.

mating (noun)	sexual activity (noun)
the act of pairing a male and female for reproductive purposes	activities associated with sexual intercourse